(a) Field of the Invention
This invention relates to an improved process for preparing 3-(4-pyridinyl)-2-cyclohexen-1-oxime, a rosoxacin intermediate, from ethyl 5-oxo-2-[(4-pyridinyl)carbonyl]hexanoate.
(b) Description of the Prior Art
Gelotte et al. U.S. Pat. No. 4,111,946, issued Sept. 5, 1978, shows two sequences for converting ethyl 5-oxo-2-[(4-pyridinyl)carbonyl]hexanoate to 3-(4-pyridinyl)-2-cyclohexen-1-one: (1) heating ethyl 5-oxo-2-[(4-pyridinyl)-carbonyl]hexanoate under aqueous acidic conditions thereby hydrolyzing and decarboxylating it to produce 1-(4-pyridinyl)-hexan-1,5-dione and then reacting said hexan-1,5-dione with a basic condensing agent to produce 3-(4-pyridinyl)-2-cyclohexen-1-one; and, (2) reacting ethyl 5-oxo-2-[(4-pyridinyl)-carbonyl]hexanoate with a basic condensing agent to produce ethyl 3-(4-pyridinyl)-2-cyclohexen-1one-4-carboxylate and then heating said 4-carboxylate under aqueous acidic conditions to hydrolyze and decarboxylate it to produce 3-(4-pyridinyl)-2-cyclohexen-1-one. The 3-(4-pyridinyl)-2-cyclohexen-1one was then reacted with hydroxylamine to convert it into its oxime, an intermediate for preparing 3-(4-pyridinyl)aniline, in turn, an intermediate for preparing rosoxacin, an antibacterial agent, namely 1 -ethyl-1,4-dihydro-4-oxo-7-(4-pyridinyl)-3-quinolinecarboxylic acid.